Please re-read http://cvxr.com/cvx/doc/solver.html#controlling-precision
For cvx_solver_settings, you need to use name value pairs for parameter names specific to the solver you are invoking.
For cvx_precision, use one of
and there are other calling methods as described in the above link.
displays the current CVX precision settings.
cvx_solver_settings provides more control and allows you to specify any parameter values the solver accepts. You need to look at the solver documentation to see the list of parameter names and how they are used by the solver.
The primal-dual solvers called by CVX often tend to get to some level of achievable precision in the solution, and the precision or solution achieved often doesn’t vary much or at all when precision parameters are adjusted over a fairly wide range of values. That is not true however for first order solvers such as SCS, which can be called by CVX 3.0beta, and only converge at a linear rate.